1. Field of the Invention
The present invention relates to a rotary engine, and more particularly to an internal combustion engine in which a piston assembly orbits continuously within a toroidal chamber.
2. Description of the Prior Art
The conventional technology for internal combustion engines is the reciprocating piston engine which has evolved and been refined over a period of some 125 years. That kind of engine is, however, subject to a number of widely recognized, severe limitations and constraints in power generation efficiency.
The reciprocating piston engine does not produce rotary motion with a constant torque arm but, rather, uses a crankshaft to convert reciprocating motion of a piston into rotary motion, with the attendant disadvantage of a variable torque arm that is drastically reduced in the top dead centre region of the piston when combustion is initiated. The result is a lack of torque and power and a reduction of engine efficiency.
Many attempts have been made to produce a workable xe2x80x9ctoroidal piston enginexe2x80x9d which provides revolving pistons mounted to a central disk to produce the desired constant torque arm, Examples of this kind are to be found in U.S. Pat. No. 4,035,111 (Cronen, Sr.); U.S. Pat. No. 4,242,591 (Harville); U.S. Pat. No. 4,683,852 (Kypreos-Pantazis); U.S. Pat. No. 4,753,073 (Chandler); U.S. Pat. No. 5,046,465 (Yi); U.S. Pat. No. 5,203,297 (Iversen); and U.S. Pat. No. 5,645,027 (Esmailzadeh).
In common with all positive displacement combustion engines, the toroidal engine must incorporate means both for compressing the intake charge and for containing the hot expanding gasses that are generated by combustion. In keeping with this principle, previous inventors of toroidal engines have usually made provision for some sort of xe2x80x9cvalvexe2x80x9d to intercept the path of the advancing piston, to retract and so allow the piston to pass by, then to close behind the piston.
In this manner, the intake charge is compressed between the advancing piston and the valve blocking its path. The compressed charge is then diverted into a combustion chamber, the valve is briefly opened to allow the piston to pass by, the valve closes and the ignited combustion gases, released from the combustion chamber, expand between the closed valve and the retreating rear face of the piston. Accordingly, each piston is propelled on a circular orbit as it passes through the valve aperture.
My study of the prior art, experiments which I have conducted and computer-assisted thermodynamic modelling results have led me to conclude that the reason none of these approaches has achieved commercial success stems from general failure to address a fundamental problem inherent in the operation of toroidal engines, namely, the loss in compression potential and the loss in air mass which occurs between the front face of a piston and a valve intersecting the toroidal chamber in advance of that piston and, likewise, the pressure loss which occurs between the rear face of the piston and the intersecting valve behind that piston. Thus, that air mass between the advancing face of a piston and the intersecting valve which is not diverted into the combustion chamber, but escapes into the toroidal chamber, is xe2x80x9clostxe2x80x9d to the useful generation of work.
In a toroidal piston engine of this general kind, some mechanism is required for opening and closing a valve seat in advance of and then behind a moving piston to gain the mechanical energy resulting from compression, ignition and expansion. Any such mechanism will take a certain amount of time to open or close and, to that extent, the piston will have travelled further in its angular rotary motion, creating and enlarging a xe2x80x9cresidual volumexe2x80x9d (or, equivalently, xe2x80x9cdead volumexe2x80x9d). This effect can lead to a loss in compression ratio, a loss in air mass, and concomitant loss of expansion pressure, in turn resulting in significant inefficiency and loss of power.
Hitherto, the designers of toroidal engines have apparently acted on the assumption that merely to block the path of the advancing piston with a valve and to trap the intake charge will generate adequate compression, with no loss of air mass, and adequate pressurization of the toroidal chamber. Prior known engines of this kind have never achieved this desired result, however, as each employs one or another intersecting valve opening-and-closing mechanism which is too slow. This results in unacceptably large residual volumes produced ahead of and behind the valve by the rapidly moving pistons.
As a specific example, the aforementioned patent to Kypreos-Pantazis discloses a rotating piston internal combustion engine in which the mechanism for opening and closing the toroidal chamber in advance of and behind a piston comprises separating walls adapted to move radially inwardly and outwardly to divide the toroid inner space into sub-chambers. The means to withdraw the separating walls to allow the passage of a piston and thereafter reinsert it is typically a cam coupled mechanically to the central output shaft of the engine to withdraw the walls periodically from the toroid chamber as the shaft and piston assembly rotates, and return springs for reinserting the walls into the toroid chamber.
A practical problem with that and with other prior art toroidal engines is that their opening-and-closing mechanisms create significant residual volume between the front and rear of the piston, resulting in entirely unsatisfactory performance. I have employed thermodynamic mathematical modelling to demonstrate the inevitability of the practical failure of toroidal engines using such mechanisms. All of the prior art exemplified in the patent literature employs either planar sliding valves or planar rotating valves, which are required to move in reciprocating fashion owing to the configuration of the toroid. At the high rotational speeds required by an engine cycle, reciprocating mechanisms are very difficult to seal and to maintain.
The same thermodynamic mathematical modelling and analysis also revealed a surprisingly drastic improvement in the performance of toroidal piston engines where the residual volumes are contrived to be made as small as possible. Indeed, the dead volume would ideally be zero but as a practical matter, of course, the moving piston and the valve in its closed position must never physically contact each other.
The practical conclusion of my analysis is that a toroidal engine of this general kind becomes usefully workable only where the volume in the compression phase of the cycle (between the piston and valve) is physically reduced sufficiently to generate a compression ratio approximating the value achieved in conventional reciprocating piston engines and the loss of air mass is minimized to achieve an efficiency comparable to conventional engine technology. That ratio, in an SI engine, typically lies in the range of between 8:1 and 12:1 or, in the case of the Diesel engine, approximately 18:1.
The fundamentally different approach I have taken to improving the performance of toroidal piston engines of this kind is to alter the geometry of the chamber section formed between valve and piston to minimize the residual volumes and thereby attain the very significant improvement in performance which was predicted by the analysis of models. For that reason, I refer to my invention as the xe2x80x9cvariable geometry toroidal enginexe2x80x9d or VGT engine. As discussed below, the aforementioned geometry can be varied by employing a rotating disk valve with an aperture that periodically intersects the toroidal chamber and minimizing the residual volumes between piston and valve.
In a first principal embodiment the reduction in the residual volumes is achieved by matching the three-dimensional shape of the piston to the valve opening. According to a second principal embodiment, it is achieved by providing a piston which is mechanically expandible and contractible, to minimize the residual volumes between the piston and the valve just prior to opening of the valve and just following shutting of the valve.
It is a principal object of the invention to provide a toroidal engine in which the residual volumes between the piston and the closed disk valve are minimized to achieve superior performance characteristics.
It is a further object of the present invention to provide a toroidal piston engine in which the volume between piston and valve in a compression phase of the working cycle is sufficiently small to generate a compression ratio of a value approximating that achieved in conventional reciprocating engines.
It is a further object of the present invention to provide an engine as aforesaid which will run smoothly with virtually no vibration.
It is a further object of the invention to provide an engine as aforesaid which is compact and which can be built as a gasoline engine running on the Otto cycle or as a Diesel engine by the expedient of reducing the volume of a combustion chamber with an adjustable counterpiston and changing the fuel system to Diesel fuel.
It is a further object of the present invention to provide an efficient, pneumatically powered rotary engine for use in environments where combustion is unduly hazardous, as an air motor providing high torque at low rpm.
It is a further object of the present invention to provide a rotary motor which can operate as a steam motor with comparable or superior performance to conventional steam turbines but at significantly lower cost of production.
It is a further object of the present invention to provide an efficient rotary engine which with a suitable injection system can be built as an engine fuelled by the combustion of hydrogen.
With a view to achieving these objects and overcoming the aforementioned disadvantages of prior rotary internal combustion engines, the present invention provides an engine having pistons rotating through a non-circular cross-section toroidal chamber which is intersected by a continuously rotating disk valve having a shutter-like cutout therethrough. Two counter-rotating disk valves may be used to decrease the opening and shutting times still further.
The shape of the pistons, the chamber through which they move and the cutout portion of the continuously rotating disk valve, unlike prior art toroidal piston motor arrangements, are designed with a view to minimizing the residual volume, thereby enhancing the compression ratios to levels which are useful in practice.
According to a first principal embodiment of the invention, the residual volumes are minimized by having the shape of each piston matched to the non-circular geometry of the toroid and having the trailing and leading edges of each piston formed with a three-dimensional curvature such that the outer surface of each piston remains as close as practicable to the interior walls of the valve cutout as the piston passes through, during operation of the engine.
According to a second principal embodiment of the invention, the residual volumes are minimized by providing pistons which are mechanically extendible and retractable, in conformity with the speed of passage of the piston through the disk valve, so as to minimize the residual volumes.